Unsympathetic is a related term of impassive.
As adjectives the difference between unsympathetic and impassive
is that unsympathetic is not sympathetic while impassive is having, or revealing, no emotion.
impassive
English
Adjective
(
en adjective)
Having, or revealing, no emotion.
Still or motionless.
Synonyms
* apathetic, phlegmatic